The present invention relates to an apparatus for the storage of a voltage analogous to an exposure parameter in photographic cameras with an electronic timer and with electric exposure measurement.
It is known to provide an electronic timing mechanism in photographic cameras, wherein the capacitor of an RC circuit is charged via a photoconductive cell. The charging takes place during exposure, and the latter is terminated once the capacitor charge has reached a certain potential.
However, such a mechanism cannot be used in many cases, for example it cannot be used if the photoconductive cell cannot be exposed to the light during the operation of the shutter. In these cases, a voltage analogous to the exposure time must stored prior to the actuation of the camera shutter, from which the exposure time is formed later on. The same holds true for spot measurements wherein the object brightness is measured only in a portion of the picture area.
Many suggestions have been advanced for such storage methods. However, all of these conventional suggestions have the disadvantage that either the storage procedure can be effected only briefly (capacitor storage) or that mechanical/electrical components must be employed permitting a quasi-mechanical voltage storage. A potentiometer, for example, can be used as such a mechanical/electrical component.
The setting of such a mechanical/electrical component has, however, the disadvantage that it requires a certain strength, and furthermore is relatively slow. Thus, a potentiometer, for example, must be brought into the correct position by a mechanical force, and other similar elements, such as servomotors and the like, also require a special adjusting force.
Therefore, the present invention is based on the problem of providing a long term storage device operating with purely electronic means and not requiring any mechanical adjusting force for the operation. In this connection, it is, first of all, of secondary importance which exposure parameter or voltage analogous thereto is stored in this storage device. This can be, for example, a voltage analogous to the exposure time. However, it is also possible for the storage to be one which is analogous to the luminous density of the object, or a voltage analogous to the luminous density of the object under consideration of the film sensitivity, and finally, this voltage can also be one which is analogous to the diaphragm.